This invention relates to an image processor which encodes image data.
In videotelephone, video conference system, or the like over communication line, encoding is an indispensable technology for the transmission of enormous amounts of image data, for communication lines are slow in data transmission. H.261 and H.263, recommendations by ITU-T (International Telecommunication Union--Telecommunication Standardization Sector), have been known as employable encoding systems. Also, other encoding systems named after the experts groups of ISO (International Organization for Standardization) have been known, such as JPEG (Joint Photographic Coding Experts Group) and MPEG (Moving Picture Experts Group). JPEG is the international standard for color still picture compression, and MPEG is the international standard for multimedia moving picture compression.
A typical image processor has an input buffer memory formed of an FIFO (first-in first-out) memory for temporarily holding input image data, a data memory formed of a static RAM (SRAM) for storing the image data transferred from the input buffer memory, and an encoding unit for encoding the image data stored in the data memory. For the realization of various encoding systems with a single image processor, the encoding unit is formed of a program-controllable processor and a change in the encoding program executed in the processor is made. The encoding unit repeats an operation of reading image data from the input buffer memory, inputting the image data, and writing the image data to the data memory, whereby the transfer of one unit (for example, one frame) of image data from the input buffer memory to the data memory is carried out. Thereafter, the encoding unit starts encoding the image data stored in the data memory.
It is difficult for the above-described image processor to transfer, at high speed, image data from the input buffer memory to the data memory because such transfer is made by way of the encoding unit.